Journal of the Royal Society of New Zealand abstracts
Taxonomy and ecology of Phreatoicus typicus Chilton, 1883 (Crustacea,
Isopoda, Phreatoicidae)
George D. F. Wilson*, Graham D. Fenwick**
*Centre for Evolutionary Research, Australian Museum, 6 College St., Sydney,
New South Wales
**Department of Zoology, University of Canterbury, Christchurch, New
Zealand; current address: National Institute of Water and Atmosphere,
Christchurch, New Zealand
Phreatoicus typicus Chilton, 1883 was the first described species of the
isopod family Phreatoicidae. The species is here redescribed using three female
specimens from the syntype series, of which one is designated as lectotype.
Until this paper, males of this species had not been described and the biology
of the species was poorly understood. New specimens of both sexes from
Canterbury Plains (South Island, New Zealand), collected as a part of a
year-long environmental survey of groundwater wells near sewage oxidation
ponds, are used to supplement the species redescription. The survey also
collected data on the biology of phreatoicids and environmental correlates to
their presence. Males of
P. typicus showed only limited sexual
dimorphism, and were similar to those of a related species,
P.
orarii Nicholls, 1944.
Phreatoicus typicus is easily separated
from
P. orarii and
Neophreatoicus assimilis (Chilton, 1894) using
characters apparent in the mandible, maxillula and pleotelson tip. Among four
wells that were subjected to detailed biological and physicochemical analyses,
P. typicus was found at only two sites. These two wells shared
substantially higher concentrations of coliform bacteria and lower fine
sediment loads than the wells that lacked
P. typicus. Thus, unsedimented
but polluted groundwaters may be providing a suitable habitat for these
isopods. Although our size frequency data for
P. typicus were biased
toward larger sizes, sufficient numbers of adults were taken to make some
general observations on life history. Well-defined cohorts changed in size
during the sampling period. Males and females achieved approximately the same
maximum length (near 20 mm) and were mature above lengths of 11.5 mm.
The iteroparous life cycle may span more than one year, and synchronous
reproduction was signaled by a large recruitment to the adult sizes during the
winter months.
Keywords Crustacea; Isopoda; Phreatoicidea; "well shrimp"; ground water;
pollution; life cycle; bacteria
(c) Journal of The Royal Society of New Zealand,
Volume 29, Number 1, March 1999, pp 41-64
PDF file of entire paper: medium quality (1681K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
